Do we need to monitor patents by other companies?

You should definitely monitor patents by others in your field for primarily two reasons: 1) such patents will determine the likelihood of you obtaining your own patents for similar devices or technology because such patents and/or published patent applications will comprise prior art which can be cited against the claims of your patent applications; and 2) you need to know if you potentially infringe any other patents. Also note, contrary to some generally assumed incorrect positions or understandings, obtaining your own patents do not necessarily mean that you are free to make, use, or sell your own patented devices or technology - to the contrary, you may be infringing other patents even though you were granted a patent for an "improvement" in your art or field. Obtaining a patent only confers the right to the patent owner to exclude others from making, using or selling the patented device or technology - it does not confer that right, of making, using, or selling, the patented device or technoogy to the patent owner.