As a business analyst, at some point you're sure to be asked to help with various stages of vendor selection and vendor assessment. For example, you might be asked to help with the initial build-or-buy decision, preparing the Request for Proposal (RFP), or the evaluation of vendor demos or proofs of concept. Ultimately, you may even be asked to help select the vendor.
As part of the process of assessing vendors, you'll need to analyze the requirements that each vendor solution meets. You'll need to know the priority of the requirements, how thoroughly the vendor's solution meets them, whether the vendor solution fails to meet critical or high-priority requirements, what workarounds exist for these requirements, etc. You'll likely need to apply decision analysis tools to help the business choose the best solutions.