Your message is a little confusing as to whether you're applying or are thinking ahead to the future after getting on disability. But anyway, I agree, while applying, the consensus is to not work at all. The reason is that then you will have to prove if you can work a little, why can't you work full time. This makes it much harder to prove than, "hey, I can't work at all, so give me disability already".
Once you're on, there are two income limits to keep in mind. One is called the Ticket to Work Program limit (TWP) which is lower than the Substantial Gainful Activity limit (SGA). Let's say that the TWP limit is $500 and the SGA limit is $1000 per month. If you make over $500 you will use up your TWP benefits, which is something like 9 months out of every 5 years where you can be making a full time work attempt while still getting SSDI payments and Medicare.
If you go over the $1000 a month (SGA), this will signal that you're well enough to work full time and you'll get booted off SSDI.
As long as you stay under those limits, SSDI actually encourages you to work. In fact, I got a automated phone call the other day about a work from home opportunity, apparently sanctioned by SSDI (call center type work for $9 an hour).