Sequencer is always useful for molecular biologist in modern era of molecular biology. For microbiologist it would be of special importance for the identification of microbes based on 16S rRNA / 18S rRNA gene sequence and also for many other purposes.
But and big but, if you doubt that you or your collaborators or your institute would use it routinely, then its not a good idea to buy it because its quite expensive and rather than buying a sequencer, one can buy some other routinely useful cheaper instruments. Nowadays, you can get sequencing done commercially in 2-3 days!