I do very projects directly in breadboard. Sometimes I need to leave a circuit mounted on the breadboard for months (as it would take a lot of work to disassemble and reassemble). Is this healthy for breadboard contacts (they will not lose strength)?
LOL... Only months, you say?
I have projects
in use, inside cases even, that are still in breadboard form, and have been for
decades awaiting that "someday, I'll solder up a permanent one" moment, but still work fine.
As for the breadboards themselves? Yeah, if they are at least half decent quality, they don't really care if you leave something "normal" in them, like connecting wires or a DIP IC, although you do kind of wreck the holes a bit when you shove big things like TO-220 leads or big, fat, high wattage resistor leads into them. With most, like the Wishboard ones though, you can even peel off the back foamy and pull out damaged contacts and squeeze them back together to increase clamping if you want to after horrible abuse.
I've had to replace several of the individual row boards on the metal backplates after some brilliant stunts like doing mains-connected projects with un-optoisolated TRIACs shorting out, blowing up entire rows of 7400 series logic, usually taking out the parallel port I/O card in the attached PC or something also, leaving very crispy, melted Wishboards with evaporated springies and black sooty, scortchy skidmarks on top.
Oh, yeah!... Fun times!!