The short answer is "no, it is not". In fact, sometimes it is counterproductive.
In many cases the attorneys withdrew information in order to justify their
outrageous fees and artificially extended and complicated the process.
In too many cases the attorneys (especially big law firms) made mistakes that caused huge delays or even rejections: you cannot sue the attorney for making a mistake, so their motivation to avoid mistakes is not very high, especially if you paid upfront.
Once you file the application (which is very easy to do), you will get the same notifications that the attorney will get.
You will have to do all the work:
An attorney is worth your money only if the contract says that
If you hire an attorney, the only work that you should do is to obtain all the required documents from your government's agencies, and that's already a lot of work. Unfortunately, your attorney will also make you do all the work that they could do: fill the forms with the appropriate data, read the instructions on how to fill those forms, click here and click there, print, scan, upload.
Most immigration attorneys don't even seem to know which documents are required. You will be told at the last minute that some document is essential (e.g., for a while attorneys routinely asked their clients to make a copy of their tax returns when in fact US consulates did NOT accept copies of tax returns and instead required IRS transcripts, which can be obtained for free from the IRS website... if only the attorney told you about it).
Something very annoying will happen very soon: the psychology will change dramatically once you start the process because the attorney can blame YOU for any delay in the process if YOU don't do what they ask YOU to do. Let's say that someone needs to scan and upload a document and you politely ask why they can't do it, since they have machines that you don't have. They will politely reply "Note that any x y and z on your part may result in a delay in your application process". Your immigration attorney will require you to behave in ways that simplify their work; and, whenever you don't, they will subtly imply that this would cause a delay.
Keep in mind that the attorneys need to justify their outrageous fees: the longer your green-card process takes, the more you will feel that their work was worth the money (even if they did nothing most of the time). If the green-card process lasted only a couple of days, you'd feel cheated, right? That's one reason why it doesn't last only a couple of days! The longer it takes, the more likely that you'll recommend your attorney as a hard-working professional who stood by you during an endless bureaucratic nightmare. Bottom line: keep in mind that your attorney has little motivation to speed up the process.
When you are finally summoned to the interview at the US consulate, that interview lasts only a few minutes. No, they don't ask you tough questions about underwear and sex! And no they don't care about your photos on Facebook. If that's what your lawyer told you, he doesn't even know how to use Google, because you can easily google it and find reports from people who actually went through the interview. The consulate's officers are much more interested in making sure that you will not end up on welfare. Therefore they will ask you questions about your financial status and your sponsor's finances. If you have never gotten in trouble with US law, that's all they care for.
Contrary to what the US consulate may tell you, you are NOT yet approved. The final approval happens at the US airport the first time you enter the USA, and it can take several hours of interrogation (meanwhile nobody is protecting your luggage and your family and friends outside are not informed of what is happening to you). Very few immigration attorneys prepare you properly for this grueling process.
If you are applying as a spouse, and you've been married for less than two years, don't do it: you'll only get a two-year "conditional" green card and you'll have to renew it after two years. If you wait until the second year of marriage, you'll get a ten-year green card.
How to choose an immigration attorney? Choose the dirt cheapest one. They all make mistakes, they all make you do all the work, they all take advantage of the situation. And you don't really need one. The reason to get an immigration attorney is to have someone who doublechecks what you do at every step of the process, but this could also be done by any friend who went through it. And i would trust the friend over the attorney if the friend went through it recently.