Do you keep your Transformers manuals?

[Tha_Phantom]

For the most part, no. Pretty much any modern instructions go in the bin.
I've kept some from RID2001 and Armada for nostalgia. In the case of most G1 reissues I will ditch the box, but keep the bag with instructions and accessories together rather than letting all the accessories get mixed up together in a pile.
If I ever get stuck with a toy I just refer to YouTube anyway, my brain finds it hard to follow instructions on paper for some reason.

[Ode to a Grasshopper]

Yeah, I keep the cardbacks/flattened boxes and instructions, just in case I ever end up selling them and people want the extra bits. The instructions are good for a friend's kids as well, they're pretty good re. how bits work and know to Handle With Care but having the instructions as backup options is still helpful sometimes.

That said I prefer to buy loose/used, so a lot of them don't have instructions anyway.

[Seraphim Prime]

I've kept all my manuals - previously they were kept in plastic sleeves in ring-binder folders, but the recent fold-out style instruction sheet has made that difficult. Currently the more recent ones are organised in a shoe box until I can work out how to file them properly.