Has anybody seen a schematics like that:
I have no idea what could be the sense of that? Signal distribution / amplification? I found it an older schematics I'd like to understand...
Thanks for your help !
Cheap non-inverting buffer and signal load isolation. That's it.
Why? Don't know. That depends on the sections before and after (not shown)
Another possibility would be level conversion. The 74LVC08 has 5 Volt tolerant inputs.
Cool!
Thanks for you answers! 
Another option, for when you wanted to deploy a load isolation buffer is the 74HCT07, which at places I have checked actually costs a few cents more... and if you only need 4, you have 2 extras just hanging out there and require special attention to make them not floating inputs.
The general idea here is that a single output gate has a limited ability to supply current to loads. The joined buffer arrangement allows that single gate to have much higher "fan out" by recreating the signal on 4 output... each with the load capacity of the original.
By joining the dual inputs in the 7408, you are just making a single channel buffer arrangement and if you only wanted 4, its perfect.