Difference between Layer 4 and Layer 7 VIP ?

There is alot of good documentation on F5's support website which details this. Here is just one of them:

https://support.f5.com/kb/en-us/solutions/public/4000/700/sol4707.html

One of the differences is by applying a http profile to say, a standard profile. In this case the F5 will parse layer 7 traffic (http) based on the settings in the http profile. A performance layer 4 (fastL4) profile forwards packets on a packet by packet basis (extremely fast): and does just that, at the socket level.

Biggest advantage of a layer 7 VIP, standard with a HTTP profile as the example, is the ability to both manipulate data inside the payload such as headers, cookies, content, etc.. as well as make decision on that content. The biggest advantage of Layer 4 VIPs is the ability to make decisions just on the packet basis and can be offloaded into specialty hardware bypassing the CPU for most of the conversation, a PVA chip.