Collecting code coverage information makes the code larger and slower, but still workable. Compiling with binary flags results in code that is faster and smaller than code compiled with counters (see generate-code-coverage and with-code-coverage-generation) and it also reduces the size of the data that code-coverage-data needs to keep. On the other hand you lose the counters, but if you do not need the counters it may be useful.
LispWorks User Guide and Reference Manual - 13 Feb 2015