Generalisations on buffer placement
These are generalisations only. Nobody needs an additional buffer but you might want one if your sound requires some strength, edge and brightness. Adding a buffer affects the whole resultant sound, but where you place it will affect each individual pedal differently.
Delays and Reverbs
Usually not a big issue with buffers unless you want to keep a very dark or analogue sound. True bypass pedals can be buffered before or after to taste. Buffered bypass pedals shouldn’t need additional buffers.
Can work well placed as the last OD in your chain, keeping its buffer after all the other fuzz or drive, but before your delay and reverb. Can make fuzzes sound harsh. Could create a conflict placement with your modulations.
True bypass pedals can gain clarity with a buffer afterwards. Buffered bypass pedals can cause issues for drives placed after.
True Bypass OD
A buffer before can brighten or add edge, but the buffer is usually better placed after drives. Overdrives tend to like seeing your guitar, not a buffer.
Usually hate buffers before them. Germanium fuzzes usually need to be first after the guitar. Brighter or harsher with a buffer after.