I'm not a professional astronomer but I do work in Astronomical research and work with a great many professional astronomers. There are 2 categories of professionals - the theorists and the observers. The theorists, in general, have never and will never use a telescope of any kind. Most have no idea how to even operate a telescope (I kid you not).
Observational astronomers either use telescopes directly (ie hire out time on telescopes for programmed work) or form research groups where they directly rely on observational data from others (including amateurs). I am a member of 2 such groups (BINAST and MicroFUN) where I supply photometric data in the search for Binary Asteroids and photometric observation of Microlensing events in the search of Extra Solar Planets.
'Small' telescopes is a relative term. Amateus with scopes as small as 8" and CCD cameras are more than capable of assisting in research areas such as Supernovea, Cataclysmic Variable Stars, Binary Stars, all forms of Planetary Sciences and in particular Comet and Asteroid research and much, much more.
Why are 'amateur' scopes used? They are cheap to access (ie free) and the professionals can still control the quality of the data that they get.