First, keep in mind that "1 IP is bad" and "get as many IPs as possible" are not really the only options. What I think is actually the case is that there's some diminishing returns after the 2nd IP, and very large diminishing returns after the 3rd. It's not really worth getting 4 IPs in most cases, and frequently not worth getting 3, but it is worth getting 2 with a few exceptions.
The first exception is if you aren't actually interested in being good at combat, and are an adept. Increased Reflexes is really expensive, and 'ware costs you IPs. If you're a mage, you can get cheap IPs from a sustaining focus, if you're a mundane you can get cheap IPs from Wired Reflexes 1, if you're a technomancer you can just use VR.
The second exception is if you are really tight on resources at character creation and are willing to just use drugs (cram/jazz) and/or suffer some until you can afford to upgrade later. This is mostly going to be if you are a mundane who wants to get a lot of high-cost 'ware aside from Wired Reflexes, like a hacker who wants a lot of cyberlimbs. You then really want Synaptic Boosters, and it blows to have to throw out and replace 80000ny SB 1. If you're an adept, you should just get the adept power then lose it when you get SB.
As far as the diminishing returns go: 2 IPs is twice as many as 1, and the 2nd IP comes up very often. 3 IPs is only 50% more than 2, and the cost is usually about or a bit higher than 50% more than the second: 2->3 for wired/MBW, .5->1 for SB, 1.5->2.5 for Increased Reflexes. All of those also give +1 reaction, which is good. On the other hand, though, the 3rd IP both doesn't always come up, and is less important than the 2nd - there's a good chance the fight has already been decided by then.
The 4th IP is only 1/3 more than 3, and costs way more than 33% more than the 3rd. WR/MBW jump from 3 to 5 essence, SB jumps from 1 to 1.5, Increase Reflexes jumps from 2.5 to 4. They do offer +1 reaction, again, which at a certain point is worth it (and it's not as bad for adepts if they can get a Way, or Way+Cheese Gaesa to discount it), but it's still a very large investment for a marginal improvement.