This depends on the precise marketing activity. In some cases, it’s necessary – like with SEO (search engine optimisation). This is because your law firm’s website needs to publish content that’s similar to (or higher in quality and longer than) your competitor(s) for relevant keywords to (potentially) rank higher than them for that specific keyword. In order to be competitive in this space, you will generally need to expand your website at a similar rate to or faster than your competitors. It’s very important that you don’t exactly replicate your competitors’ work, however. Copyright implications aside, search engines penalise websites for creating content that is too similar to an existing site. It’s called ranking cannablisation and it leads to incredibly poor visibility outcomes.
In other situations, it can be counterproductive and expensive. Pay-per-click advertising, for instance, is less effective and more expensive if you reverse engineer your competitors keywords exactly, since you’re all bidding on the same searches. In this case, unless you’re in a position to pay for more expensive ads, you’re possibly better off thinking outside the box.