Convert binary string to decimal number
Well, first of all the description is wrong.
strbin_to_dec() should be strbin_to_i(), because it parses a base-2-number, instead of converting it to base-10.

Next, refrain from using your own defines as much as possible, if there is an appropriate type already.

Third, assuming correct input is generally naive. Assuming corrupted or malicious input is far wiser.
Your code breaks if any character is neither 0 nor 1, or if the number is too big for an unsigned.

Finally, it's more straight-forward to parse from beginning to end, only needs a single pass, and is probably due to both reasons slightly more efficient, if you really care. Still, what input you get might be important to the determination.

Regarding your question whether byte-operations are faster than wider operations, probably only on 8bit-microcontrollers or the like.
Still, micro-optimisations are hard to do correctly, and have hardly any significant effect, especially if you don't know what to optimise for: Source clarity (should be the default), source size, compiled code size, code throughput, memory bandwidth, ...
Let's hope you chose the right optimisation-options, or the point is moot anyway.