"Do you think you need to use a heating mat for seed germination in winter?"
need: require (something) because it is essential or very important.
Hmm.. The word "need" is an interestingly tricky one. People often use the word "need" for things which they really don't need, but simply would prefer to have. As an example, if my boss is telling me to do something that I don't want him/her to do, and I tell them "I need you to shut the fuck up and get out of my face right now!", is that really a need? Of course it would be much better if the curtly implied request was acknowledged, however it may not be "needed".
So, in terms of the seed, I guess the "need" would depend on your specific environmental conditions. In a tropical heated greenhouse, for example, a heated mat would not be needed, although it might help. In contrast, germination in a cold garage, a heating mat would not only be preferred, but it might be required (needed), in order to not deter germination and growth.