In BDSM, a switch is someone who participates in SM activities as both a Top and a bottom, or possibly in D/s activities as both a Dominant and a submissive. A switch will be the Top on some occasions and the bottom on other occasions, not necessarily with the same partner. Switching within a scene, or even during a session is very rare.
With that said, there are some that will make you believe that if you are a Dominant and you like your submissive running their nails down your back or biting you while engaging in sexual play then you are a switch. That is false. The same can be said for the submissive that likes to inflict pain on their Dominant from time to time with their Dominants permission. If there is never a reversal of power exchange then you have NOT switched roles.
To throw another big one out there, I am a Dominant who is also a Sadomasochist. I am more a Sadist then a masochist but it is still a part of Me. From time to time when life throws me under the bus, I can get down and feel the need to have a release from the bottom position. My submissive does not have a Dominant bone in her body but does have some Sadist in her. What I will do is lay out my impact toys for her. I will explain to her what I am looking for and give her detailed instructions of what I need her to do. she will follow my instructions and do what I have requested of her. When the scene is done, she will provide Me with aftercare. At no time did My submissive take the Top role where she was making the decisions beyond what I had instructed. At no time did I submit to her wishes and wants. Therefore we didn’t step out of our normal D/s roles.
Is being a Switch a bad thing? Absolutely not! There are tons of Switches that have been in the lifestyle for a VERY long time. Most can be very effective in either role but usually have a preferred role. Think of it this way, if your Dominant is a Switch then they will most likely understand what it is like to be on the bottom then a Dominant that has never been there.
BDSM is based on a high level of respect and we have to understand that the way you do something in this lifestyle is probably different then other people. This doesn’t make it right or wrong for either party, it just creates a learning experience for everyone.