Everyone has a drawer full of knives- a knife for every purpose- a bread knife, a chef's knife, paring knife, maybe a cleaver and of course a set of bread & butter knives.
Which one would you use to slice a tomato?
The safe bet is you wouldn't be using a bread & butter knife. One could compare the skin of a fresh tomato with the wrapper of a premium cigar. Both serve to protect its delicate interior. A dull knife is like a cheap cigar cutter.
The basic-plastic cigar cutters are a great promotional item and for the first 5 or 10 cuts might do a decent job trimming the end of a cigar. They are also great to have as an emergency cutter for the car or your travel bag (check in luggage).
Past that they shouldn't be seen anywhere near your cigars.
The iris action of a curved double-bladed cigar cutter comes in from gentle angles that encase the contour of the cigar to deliver a more surgical cut leaving behind no rough edges of tobacco, no broken, shattered or unravelling cigar wrapper plus you have much more control over your cut.
Above all that, your cigar will look better and feel better in your mouth, in your hand, in the ashtray and the likes of the Xikar cutter will last you a lifetime.
Prices for a good too, a decent quality Colibri or Xikar cutter start at around $70- why wouldn't you own one? There's little point spending $40 to $60 on a single cigar, only to ruin it right off the bat with a dull cigar cutter.
Personally I have owned a Xikar Xi2 now for well over 20 years, that lifetime warranty and the ability to get it replaced when the blades get dull has made it one of the best investments in my life.
These days we are lucky to have a wide-range of cigar cutters available to experiment with too;
Double-blade guillotine cigar cutters (Xikar Xi1, Xi2, Xi3; Colibri Quasar etc)
Cigar scissors (Xikar MTX Multi-tool)
XO double-blade guillotine cigar cutters (Xikar XO)
Straight cigar cutter (Colibri S-Cut)
V cigar cutters (Firebird Viper; Xikar VX2; Colibri Quasar; Colibri SV; Colibri V-Cut)
Punch cigar cutters (Xikar 9mm or 11mm punch cutter; Colibri Three-in-One punch cutter)
So as you can see there is a wide range of possible cutters to experiment with; the best part is having a couple of decent quality cutters and learning which cigars taste better with a different cutter.