Smash everything with the same tool
This generally manifests itself as defensibly using familiar tools, frameworks, even languages with the rationale revolving around familiarity.
If you can only have hammers, pick the right one for the job
A tenet of Sledgehammerism is a firm belief that one thing is better than other things in the same category, usually equating to the largest, most powerful, and most mature in it’s class. A common example of this is MVC frameworks. There are many choices in any language for any platform, but some will be considered ‘better’ purely for reasons of familiarity or convenience. While this may be true, it’s also generally considered bad to mix MVC frameworks - they have a tendency not to interact in a pleasant way. So what ends up happening is bolting on an entire system just to use some small and possibly trivial part of it, just because that’s perceived as the quick and easy way forward. The effect of this it to significantly grow the codebase with dependencies and their artifacts.
If you can only have one hammer, pick the right job
Sledgehammerists will go out of their way to use what they know, and if they only know one thing (for example, Delphi / Object Pascal), then they will only work on compatible projects. This further compounds their situation by limiting their exposure to other technologies and prevents them from ‘acquiring new hammers’.
Encouraged by complexity
It is in this regard that Sledgehammerism shares elements of Librarianism, and that is it often at odds with Purism unless the hammer in question is the platform itself. Indeed, it’s entirely possible to select a product or platform that is far too complex for the task in question for exactly the same reasons as adding a heavy dependency - familiarity.
More complex, more configuration
A side effect of Sledgehammerism is a shift in the code/configuration ratio. This paradigm has a tendency to see a significant increase in configuration files to control the behaviour of the system.