The short, cop-out answer is: It depends.
Longer explanation is:
It depends on the type of novel you're writing, and also on your skill level as an author. It's possible, and common enough, to have none if you're writing the kind of novel that's epistolary (written communication, eg. letters, reports, postcards) or a monologue from the main character(s). But I suspect that's not what you're talking about.
As far as I know - and I'm happy to be corrected here - this is rarely done because it breaks so many rules of storytelling. Sure, dialogue can move into padding out territory, but that's what edits are for - to cut ruthlessly and rewrite until you've conveyed the information in the least amount of words.
Summarising a speech from time to time is fine, when there's nothing noteworthy about it, and detailing the dialogue wouldn't give the reader an expanded view of the world, the characters, or the plot. I just wouldn't cut it out completely.
Once you start reporting or summarising speeches, you're moving from "show" territory into "tell" territory. A single phrase can show the reader so much about a person and their current state of mind, that would take an author many more words to describe if they're merely reporting. For example:
Reported speech: He asked her what she was doing.
Dialogue 1: "What'cha doin'?"
Dialogue 2: "What the bloody hell are you doing?"
Dialogue 3: "W-w-w-what are y-y-you doing?"
Dialogue 4: "If I may be so bold, may I ask what the young Miss is doing?"
Dialogue 5: "By the bloody battleaxe of the wargod Sarnis, what on earth are you up to now?"
And that's only a few examples without any kind of context, action or dialogue attribution that will add more texture to such a simple question.
I'll admit, it is possible to cut out all dialogue in a novel and simply summarise everything. Is it usually the best way to get a reader invested in a story and connected emotionally? No. Is it usually the most economical way to convey one character's thoughts and feelings about another? No.
If you're a master storyteller, you may well pull it off, because after many, many years of experience you'll know it's the best way for your story to be told. You'll also know the best way to break the rules, since you understand the rules. If you're still starting off, however, I'd be a lot more cautious about doing something so "avant-garde".