Pictures are key tool in visual communication as saying goes
A picture worth a thousand word.
Visual aids such as diagrams help in communicates key concepts and ideas. Diagrams are key in technical documentation and writing that breaks down concepts in order to communicate to others. In Natural Language Processing (NLP), we diagram sentences to illustrate the steps of a process in programmatically understanding language. When presenting one a either technical or non technical visual aids augment spoken substance to help communicate ideas. It is an essential too particularly in the system/software architecture.
Slide presentations help storytelling and having slides with diagram help communicate many logical structures in a system either it is cloud infrastructure and its many network topologies, security zones, or CI/CD pipelines and service dependencies.
Diagrams shows context and dependencies across complex systems and help visualize an evolving architecture. A detail diagram answer important questions about compatibility, interoperability, and other key -ilities that Architects are trusted to think through.
So there is an importance in diagraming, but what tool? There are many tools in market place. IBM Rational was pioneer on defining a language for visual aid for software system. They continue to build tool. There are many other new tools that are easy to use that helps an architect to draw simple to complex diagrams.
Rational tool is very powerful but hard to master. Having said that the first 4 in the list is my go to choice.
Diagrams.net / Draw.io
This tool is very versatile and allows to embed your diagram into your Wiki of choice.
Lucidchart
This is a also a powerful tool that allows your embed your diagram in wiki as well.
Magic Draw (a.k.a)
This is an expensive hidden treasure. It pioneered linking diagram thus you can move from diagram to diagram that is abstract to details through links so that the diagram is not complex.
https://www.nomagic.com/products/magicdraw
Enterprise Architect
This tool competes with Magic on the diagram links. It is a good tool. It has been gaining grounds with the Architect as it is a cost effective tool.
Gliffy
It is like a visio but online tool.
Omnigraffle
IBM Rational
https://www.redhat.com/architect/diagramming-tools-cloud-infrastructure
Conclusion
Whether you are an Architect or developer or a business analyst, diagrams enhances your ideas and vision. These architectural diagrams of complex systems reflect multiple views of the complex reality of IT infrastructure. All of the tools listed here will give you a great way to start designing images that tell the story of system architecture. It really depends on your budget and linking of a tool.